1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device. Note that semiconductor devices herein refer to general elements and devices which function by utilizing semiconductor characteristics.
2. Description of the Related Art
As a material having semiconductor characteristics applicable to thin film transistors, a metal oxide has attracted attention, and thin film transistors in which a channel formation region is formed using such a metal oxide having semiconductor characteristics are known (for example, see Patent Documents 1 and 2).
Further, in accordance with advance in performance of a semiconductor device, high-speed operation of a transistor has been required. For example, a technique has been reported in which high-speed operation is achieved by shortening of a channel length of a transistor (for example, see Patent Document 3).